More specifically, the invention is concerned with the type of vibration testing apparatus which comprises a vibration generator unit which is coupled to a slip plate supported on a bearing system, by means of a driver bar. The element or component to be vibration tested is mounted on the slip plate which is supported, e.g. by means of hydrostatic bearings, so that it will slide to and fro in a horizontal plane along a preferred axis of oscillation with little friction, and the slip plate is coupled to the vibration generator by means of the driver bar. In operation, the vibration generator is disposed so as to vibrate along a horizontal axis, but is mounted so that it can be pivoted to a position in which it is capable of oscillating about a vertical axis. In this position it is coupled from the slip table and can be used for other vibration testing operations. Thus, the driver bar which serves to couple the vibration generator to the slip plate is connected to the latter in a disengageable manner, for example by means of bolts, or preferably by means of expander pins which serve to transmit the vibrations from the vibration generator to the slip plate more effectively whilst tolerating dimensional differences due to changes in temperature. When it is desired to pivot the vibration generator about its axis so that it can vibrate along a vertical axis, it is necessary to remove the bolts and/or expander pins to disengage the driver bar from the slip table.
One construction of driver bar according to the prior art comprises a slotted member and the edge of the slip plate is engaged within the slot so that the adjacent arms of the member embrace either sides of the slip plate and receive the connecting bolts and/or expander pins which pass through the arms and the slip plate. With such a construction, when it is desired to disconnect the vibration generator from the slip plate, it is not only necessary to remove the bolts and/or expander pins connecting the driver bar to the slip plate, but it is also necessary to provide sufficient lateral displacement of the slip plate so that it can be moved by a distance to free its edge from the slot in the driver bar and thereby permit the vibration generator coupled to the driver bar to be pivoted clear of the slip plate. This in turn necessitates the use of special bearings for the slip plate in order to provide the necessary degree of lateral shift.
According to another prior art arrangement, the driver bar is of a cantilever type which is arranged so as to overlie only one surface of the slip plate and is connected thereto by means of the connecting bolts and/or expander pins. Whilst such an arrangement facilitates the pivoting of the vibration generator from its horizontal vibration position to its vertical vibration position, since it is only necessary to remove the connecting bolts and/or expander pins to enable the vibration generator to be swung away from the slip plate, such a construction possesses the disadvantage that the vibration force is not applied symmetrically about the median horizontal axis of the slip plate, whereby eccentric or off-centre vibration forces may be applied to the slip plate and hence to any component to tested mounted thereon and this in turn can lead to be difficulties and undesired results.